Where do you put this code? ...In a combobox no code is needed to set its variable!

I have an input form
In the combobox I have a list of latin names to select a plant which then will show with its appropriate entries in the form. That's no problem. At the left bottom of the form I have some buttons to browse the plants. Their entries are then shown in the form - no problem either. Only the combobox doesnt show the new value.
In the shown example the entry Actinidia delicosa (like in the field Lateinischer Name in the upper left) should appear in the combobox - but it doesn't!

where i is the number of the actual plant. This is increased by one and the appropriate line of the file containing the data is read. The subroutine convert converts some special characters from HTML code to ANSI. The data fields in the text file are separated by +++. This line then is split and the array [Ergebnis] contains the different fields. [Ergebnis1] contains the latin name (which it really does as I can watch in the debug window and the field Lateinischer Name is correctly filled with [Ergebnis1]). But the combo box remains unchanged. Why?
Below the definition of the ComboBox:
I changed the Variable contains from item number to item text - no change.